Reference circuits are commonly used in many devices. Generally, bandgap circuits are used in combination with startup circuits. These startup circuits, especially with high voltage applications (generally between 6V and 40V) like automotive applications, can consume great deal of power. Some examples of conventional circuits are as follows: U.S. Pat. No. 6,222,399; U.S. Pat. No. 7,286,002; U.S. Pat. No. 7,323,856; and Khan et al., “Low Power Startup Circuits for Voltage and Current Reference With Zero Steady State Current,” Proceedings of the 2003 International Symposium on Low Power Electronics and Design, pp. 184-188, August 2003 (“Khan”).
One configuration disclosed in Khan and U.S. Pat. No. 7,323,856 employs a capacitor in the startup branch. Essentially, the capacitor (as well as internal resistances) are employed due to their resistor-capacitor (RC) delay or “time constant,” which provides a peak current to start the circuit. A problem with this system is that if the supply ramp is about the same order as the time constant then circuit may not startup. Thus, this configuration does not possess the desired characteristics.